Abstract

The temperature dependence of the dynamic relaxation rate in epitaxialthin films is investigated in the temperature range from to the critical temperature with and without an applied dc magnetic field, and the dependence on the dc field at is measured at fields up to . It is shown that the experimental results are in good agreement with the vortex lattice pinning model proposed previously which considers the main pinning centers in thin films to be threading dislocations on a network of low-angle grain boundaries. From the results of the experiment it is concluded that the influence of thermal fluctuations on the vortex pinning by threading dislocations and on the magnetic flux creep near is not so crucial as in the case of pinning by extended linear defects in thick films or single crystals. Estimates are made which show that this fact can be explained by a transformation of the Abrikosov vortices into Pearl vortices when the magnetic field penetration depth becomes greater than the film thickness as the temperature approaches a critical value. Because of this, the mechanisms of pinning and flux creep in thin films are of a substantially collective character even in extremely weak magnetic fields and at temperatures very close to .

This study was supported in part by the “Nanophysics and Nanoelectronics” project of the program “Nanostructure systems, nanomaterials, and nanotechnology” of the National Academy of Sciences of Ukraine, and also by project VCs/95 of the Presidium of the National Academy of Sciences of Ukraine.